Report Date - February 26th to March 3rd, 2024

Prepared By: Summer Manestar & Andrew Kamerosky

For the week of February 26th, 2024, the change in estimated median Chlorophyll A (ChlA) varied across most of the Indian River Lagoon (IRL). Imagery from February 25th was compared against February 28th (Table 1).

All lagoon segments ended the week with median ChlA concentrations in the low-level bloom range between 6 to 20 µg/L. The Southern Mosquito Lagoon (SML), Northern-North IRL (N-NIRL) and North-Central IRL (N-CIRL) had a slight decrease in ChlA, while all other lagoon segments had an increase in ChlA levels.

There was one (1) usable Sentinel-2 scene and three (3) usable Sentinel-3 scenes during this period.

There was one (1) scene from Sentinel-2 that was usable for detection of bloom activity the week of February 26th (Figure 1). Of note in this scene is the presence of medium bloom activity in the Southern Mosquito Lagoon (SML).

Figure 1 - Processed Sentinel-2 imagery for February 27, 2024

Sentinel 3

There were three (3) scenes from Sentinel 3 that were usable for detection of bloom activity the week of February 26th. However, because the scenes were on consecutive days, imagery from the week prior was used to present a more accurate comparison. (Figure 2, Figure 3). The following analysis focuses on scenes from February 25th to February 28th (Figure 4, Figure 5). 

Figure 2 - Processed Sentinel-3 imagery for February 25, 2024.

Figure 3 - Processed Sentinel-3 imagery for February 28, 2024.

Figure 4 - Sentinel 3 estimated Chlorophyll A (ChlA) Levels in Micrograms/Liter (µg/L) for February 20th and 25th, 2024, over sections of the Southern Mosquito Lagoon (SML) and North Indian River Lagoon (NIRL). The box plots represent the range of estimated ChlA values for each Basin, with the boxes showing the second quartile, median, and third quartile, and the whiskers representing the first and fourth quartiles.

Figure 5 - Sentinel 3 estimated Chlorophyll A (ChlA) Levels in Micrograms/Liter (µg/L) for February 25th and 28th, 2024, over sections of the Banana River Lagoon (BRL) and Central Indian River Lagoon (CIRL). The box plots represent the range of estimated ChlA values for each Basin, with the boxes showing the second quartile, median, and third quartile, and the whiskers representing the first and fourth quartiles.

Table 1 - Sentinel-3 estimated median ChlA in µg/L and percent change between February 25th and 28th, 2024, by IRL Basin.

SJRWMD IRL Continuous Monitoring Stations

The St. Johns River Water Management District (SJRWMD) Continuous Monitoring (CM) stations measured Chlorophyll Reflective Fluorescence Units (RFU). (Figure 6, Table 2). 

Current and historical data are added to the SJRWMD’s database continuously; subsequent visits may reflect such additions or revisions. SJRWMD provides no warranty as to the accuracy, reliability, or completeness of these data.

Figure 6 – St. Johns River Water Management District (SJRWMD) Indian River Lagoon (IRL) Continuous Monitoring Station Relative Chlorophyll A (ChlA) readings for the week of February 26th, 2024.

Below are the estimated ChlA levels measured by SJRWMD continuous monitoring stations for the week of February 26th, 2024 (Table 2). The Continuous Monitoring Station data is reported hourly by SJRWMD, and this report provides the 95th percentile of RFU for a given day. 

Table 2 - St. Johns River Water Management District (SJRWMD) Indian River Lagoon (IRL) Continuous Monitoring Station Average Relative Chlorophyll A (ChlA) 95th percentile levels for the week of February 26th, 2024.

The availability and usability of satellite imagery is contingent upon both the satellite being overhead and low cloud cover. The orbits of the Sentinel satellites will sometimes cover a portion versus all of the Indian River Lagoon. Cloud cover can also result in only portions of the Indian River Lagoon (IRL) being visible. Table 3 below lists the availability of Sentinel imagery and its usability for Harmful Algal Bloom (HAB) analysis.

Table 3 - Sentinel-2 and 3 imagery availability for the week of February 26th, 2024.

N - Imagery Not Available

Y - C - Imagery Available, Cannot Use Due to Cloud Cover

Y - P - Imagery Available, Only Partial Imagery of IRL

Y - G - Imagery Available, No Issues Over the IRL

Methods

HABs observed by this project are defined as over 80 Micrograms/Liter (µg/L) Chlorophyll A (ChlA) (as estimated by a calibrated Normalized Difference Chlorophyll Index (NDCI)) and persistent across the week in review. The algorithms that transform the NDCI index value to estimated ChlA concentrations were developed using a second-order polynomial equation. The Sentinel 2 (S2) equation has a Root Square (R2) of 0.81 with a Root Mean Square Error (RMSE) of 14.14 ug/L of ChlA. The Sentinel 3 (S3) equation has an R2 of 0.92 and an RMSE of 9.92 ug/L ChlA. The RMSE is a measure of the accuracy of a model in estimating values, ChlA in this instance, where a lower value is indicative of higher accuracy. It does not identify if the model consistently over or underestimates the modeled values. The equations are below:

• S2 Estimated ChlA = 297.36(NDCI)2 + 313.98(NDCI) + 36.152

• S3 Estimated ChlA = 437.07(NDCI)2 + 348.98(NDCI) + 33.928

   Figure 7 - SJRWMD Continuous Monitoring stations and IRL Basins used for S2 and S3 analysis. 

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